Product Quality,Phytochemical Profile,Bioactive And Toxic Properties Of Ginkgo Biloba L. Seed

In China,Ginkgo biloba L.trees' extensive cultivation has surpassed market requirements,as Ginkgo biloba seeds(GBS)production could reach as high as 60,000 tons per year.Therefore,there is an urgent need to find new opportunities to take advantage of the availability and use of GBS regardless of the season and overcome the situation that GBS usage only remains at the incipient phases of home-cooked recipes.This dissertation focuses on the drying and rehydration process of ginkgo seed,optimization of the best drying process and application of pretreatments prior to drying process,which will provide the basis for the long-term storage and use of ginkgo seed.The research is divided into three parts,and the specific content is summarized as follows:1.First,freeze-drying,infrared drying,hot air drying,and pulse vacuum drying were used to dry the ginkgo at 80? to reduce the moisture content to 6%.A comprehensive analysis of the four methods of drying ginkgo seed is as follows:(i)A detailed analysis of their drying kinetics(drying curve,drying rate curve,effective moisture diffusivity,mathematical modeling),shrinkage and energy efficiency(specific moisture extraction,specific energy consumption),and physicochemical properties(soluble solids,total sugar,reducing sugar,ascorbic acid,phenolics,and tannins)were performed.The results showed drying methods had various effects on different indexes and were confirmed by principal component analysis.The drying process occurred in the falling-rate period.The effective moisture diffusivity values amongst various drying methods ranged from 3.5 × 10-8 to 7.6 × 10-8 m2/s,which were within the normally expected range for food materials.The exponential model best fitted the experimental results for drying with the coefficient of determination(R2)>0.981 and root mean square error,the sum of square error,and reduced chi-square closer to zero than the parabolic and inverse-logarithmic(Log3p1)models.The freeze-dried GBS had the highest nutritional(statistically the same with the fresh GBS)and lower shrinkage;nevertheless,it had the lowest moisture extraction rate and the highest energy consumption.Hot-air dried GBS had the highest shrinkage and lowest nutritional retention.Infrared-dried GBS was superior with the highest non-tannic phenolic,proanthocyanidins content,effective moisture diffusivity,drying rates,and energy efficiency.(ii)A comprehensive analysis of dried ginkgo seeds was performed on product quality(appearance,color,rehydration ratio,texture,sensory,and microstructure),bioactive and toxic components(terpene trilactones,ginkgotoxin,ginkgolic acid,pyridoxine,acrylamide,total cyanide content).Results showed drying methods significantly influenced product quality,with freeze-drying being superior due to the minute micro structural damage,followed by infrared drying and pulsed-vacuum drying.Infrared-dried products possessed the strongest antioxidant activities and higher bioactive compounds content than hot-air drying and pulsed-vacuum drying.Toxic compounds in fresh Ginkgo biloba seed(ginkgotoxin,ginkgolic acid,and cyanide)were reduced drastically by drying.Ginkgotoxin was reduced by four-folds,and the content of acrylamide,ginkgolic acid,and cyanide in the dried ginkgo biloba seeds reduced to the scope of safety.Amongst the four drying methods,infrared drying had the shortest drying time,and its product showed higher quality and bioactive compounds content and stronger antioxidant activities.(iii)Dried ginkgo seeds using different methods rehydrated by submerging into the water at 60? for 60 min.The influence of drying methods on rehydration kinetics and quality attributes were evaluated.Results showed the Weibull model provided the best fitting for each rehydration curve(coefficient of determination(R2)>0.99,residual sum of squares(RSS),reduced chi-square(?2),and root mean square error(RMSE)closer to zero).Toxic compounds(ginkgotoxin,ginkgolic acid,and cyanide)decreased significantly while total phenolic content(TPC)and total flavonoid content(TFC)increased in rehydrated products compared with fresh GBS.The sensory score was acceptable for all rehydrated products.Besides,rehydrated products showed retention of antioxidant activities and the formation of Maillard reaction products(MRP).Amongst rehydrated products,infrared drying coupled to rehydration stood out being superior with higher TPC,TFC,MRP,and antioxidant activities and lowest enzyme activities,which were again corroborated from the principal component analysis.The present findings will offer more information in selecting the best drying method for GBS's rehydration as a snack,breakfast,or others.(iv)A Comparative analysis of dried ginkgo seeds with different dry method were performed using UV-Vis spectrophotometer,fluorescence spectrophotometer,Fourier transform infrared spectroscopy(FTIR),gas chromatography-tandem mass spectroscopy(GC-MS/MS),and electronic nose(E-nose).Results showed drying methods significantly influenced Maillard reaction products,flavor,and phytochemical profiles,while FTIR analysis showed drying methods did not change preliminary structures.The GC-MS/MS showed many phytoconstituents that led to a better appreciation of the nutraceutical,pharmaceutical,and medicinal benefits.These compounds consist of fatty alcohol,long-chain alkanes,fatty acids,carboxylic acid,sterols,diterpenes,triterpenes,flavonoids,and their derivatives.The infrared-dried ginkgo seeds had the highest(61)phytoconstituent,while pulsed-vacuum dried ginkgo seeds the least(24).Electronic nose differentiated flavor intensity of dried ginkgo seed,with freeze-drying exhibiting the least intensity.The principal component analysis combined with GC-MS/MS and E-nose differentiated samples was attested by Hierarchical cluster analysis.Infrared-dried product was superior with the highest Maillard reaction(highest A294 and A420).From the above comparison of the four dry methods,it was found that,for ginkgo seeds,the infrared drying method required the shortest time and the highest energy efficiency.Infrared dried ginkgo seed had the highest antioxidant activity,higher product quality and bioactives,while lower ginkgotoxin.Therefore,infrared drying was the preferred method of drying ginkgo seed.2.Optimize the process conditions and parameters of the selected ginkgo seed infrared drying method,based on comparing the statistical design and selecting the best of design of infrared drying:(?)Choosing a suitable infrared drying condition for dried seeds and selecting the appropriate statistical technique for the drying of seeds to improve bioactive components and desired functionality is paramount in the food industry.In this study,process parameters of the infrared dryer were optimized for dried Ginkgo seeds.The screening by Plackett-Burman design(PBD)indicated that drying time,temperature,and the distance between infrared emitter and samples were the significant factors for green-red(a*),yellowness(b*),ascorbic acid(AA),and rehydration capacity(RC)responses.However,none of the factors was significant for the total flavonoid content responses'.Hence,a*,b*.AA,and RC were used for further optimization.Rotatable central composite design(RCCD)and Box-Behnken design(BBD)optimization were performed to get a minimum AA and a*degradation,maximum b*,and RC.Both designs had acceptable models.Although PBD-BBD had a higher coefficient of determination(R2),PBD-RCCD was selected for further experiment due to a higher lack of fit and lower residual standard error.The optimum conditions using RCCD were temperature=74.6?,time=173 min and height=22 cm.Although dried ginkgo seeds had a lower physicochemical assessment,it had higher product quality,bioactives,antioxidants,and lower toxic components than fresh ginkgo seeds.(?)The PBD-RCCD to optimize the infrared dryer parameters was used to achieve higher bioactive(TPC),lower toxic component(MPN)with an appreciable MC and ?E of ginkgo seeds.The screening of factors by PBD indicated temperature,time,and height contributed significantly to moisture content(MC),total color change(?E),total phenolic content(TPC),and Ginkgotoxin(MPN).Further using rotatable centralcomposite design to obtain the optimum conditions were temperature(80?),time(159.68 min),and height(12 cm).Satisfactory results were(6.09±0.15)%,5.56±0.45,(6.25±0.38)mg gallic acid equivalent/g,and(50.57±1.10)?g/g for MC,?E,TPC,and MPN,respectively,with verification close to the predicted values.This shows an increase in TPC,appreciable ?E,MC,and a drastic reduction in MPN(5.45 fold)compared with fresh GBS.The quality assessment showed higher pyridoxine,antioxidant activities and total flavonoid,lower enzyme activity and ginkgo lic acid(10 fold),granular adhesion(from the micrograph),and satisfactory product quality.This shows the infrared-dried GBS under these optimum conditions had ginkgotoxin and ginkgolic acid contents below the level likely to cause toxicity.3.The influence of pretreatments(ultrasound(US),ultrasound-assisted osmotic(USO),pulsed-vacuum osmotic(PVO),and osmotic(OS))followed by infrared drying(optimized conditions)on ginkgo seeds were investigated.(?)After pretreatments followed by infrared drying,the rehydration,physicochemical,and product quality of dried ginkgo seeds were analysed.Results showed various pretreatment affected drying,rehydration,physicochemical,and product quality,and this was confirmed by principal component analysis.Pretreated samples had lower enzyme activity,drying,and rehydration time compared to control but a negative effect on physicochemical properties(except water activity(aw)and free amino acid(FAA)).Amongst the various pretreatments,ultrasound-assisted osmotic pretreatment(USO)had the highest solid gain and sensory attributes,lowest enzyme activities.Ultrasound pretreatment gave a better texture property,but the micro structure witnessed more shrinkage.The exponential model best fitted experimental results.Although pretreated samples' physicochemical parameters were relatively lower compared to untreated samples,aw and FAA was improved by USO pretreatments.The present study showed that a combination of USO pretreatment and infrared drying might successfully plummet drying and rehydration time,improve mass transfer,energy requirements,and improve product qualities.(?)After pretreatments followed by infrared drying,the toxicants(ginkgotoxin and ginkgolic acid),main bioactives(terpene trilactones(ginkgolide A,B,and C),flavonoids(quercetin,isorhamnetin and kaempferol)),antioxidants,and flavor profiles in dried ginkgo seeds were analysed.Results revealed that non-thermal pretreatments reduced the ginkgotoxin(3.94-6.24 fold),and ginkgolic acid(6-25 fold)contents were below the level likely to cause toxicity.Non-thermal pretreated GBS and the control(no pretreatment)results showed that the treatments used did not trigger high acrylamide levels and were in a safe range.Combining various pretreatments with ID displayed diverse effects on final products,and principal component analysis attested to the findings.The control group(no pretreatment)recorded the highest toxic components(ginkgolic acid,Ginkgotoxin,and acrylamide),terpene trilactones,and Maillard reaction products compared with various pretreatments.FTIR showed no alteration in the preliminary structure of GBS.Amongst the various pretreatments,PV had the highest flavor intensities,while the US had the highest TPC and antioxidant activities.Ultrasound treatments(US and USO)had the lowest concentrations for ginkgotoxin,ginkgolic acid and acrylamide,and flavonoids preservation.This shows ultrasound pretreatment before infrared drying can be used during the processing of ginkgo seeds.